The explosive growth of digital communications technology has resulted in an ever-increasing demand for bandwidth for communicating digital data. Because of the scarcity of available bandwidth for accommodating additional digital communications, the industry recently turned its focus to the idea of utilizing the preexisting analog FM band more efficiently to help make such an accommodation. However, it is required that any adjustment to the FM band utilization does not significantly affect the performance of the analog FM communications.
A licensing authority grants FM broadcast stations licenses to broadcast on different carrier frequencies. The separation of these carrier frequencies is 200 KHz and they are reused geographically. However, in order to account for the fairly gradual power reduction at the tails of the spectrum of an analog FM signal, closely located stations are licensed to use frequency bands separated by typically at least 800 KHz. The following provides background information on analog FM broadcast: